1. Field of the Invention
The present invention relates to an optical connector, and a connection method and a tool for the optical connector.
2. Description of the Related Art
To detachably connect the largest possible number of optical fibers within a limited space, it is necessary to realize a high density mounting of optical fibers. An approach to realize the high density mounting is described by Konishi, et al in their paper entitled "Design and Characteristics of B-1046 High Density Fiber Termination Module (FM)", Denshi-Tushin Gakkai Sogo Zenkokutaikai Kouen Ronbun-shu, 1995, P492, the gist of which will be briefly described.
The High-Density Fiber Termination Modules in a telephone exchange office are provided with optical branch modules through which the optical fiber cables connected to subscribers are optically branched to the transmission equipment and the fiber selection devices for the optical line maintenance support system. The number of optical fibers installed is increasing with the growth of the optical subscriber line network. To cope with this, it is required to increase the density of optical fiber mounting in the fiber termination modules. The optical branch modules containing optical couplers and other optical components are mounted side by side on frames in the fiber termination modules. It is, therefore, required to increase the fiber mounting density in the optical connectors as well as the mounting density of the optical branch modules in the fiber termination module.
Of the currently used optical connectors, the multi-fiber connector usually uses multi-fiber ferrules of the pin-fitting type. For an application where the ferrules, which are once coupled, will rarely be decoupled, for example, in manholes, a couple of multi-fiber ferrules are coupled together by means of simple gripping means, e.g., the clip. This type of the connector is called a MT (mechanically transferrable) connector. For an indoor application where the connectors are coupled and decouple relatively frequently, the following connector, called an MPO (multipath push on) connector, is frequently used. In the connector, a housing with a push-pull mechanism is used, are the connectors and coupled together through a connector adaptor.
In a conventional MT connector, the ends of a plural number of optical fibers are fixed to a couple of ferrules and these ferrules are coupled together, applying a refractive index matching substance. Two guide pin holes to be fit to guide pins are formed in the end face of each ferrule. The plural number of optical fibers are exposed on the end face while being located between the guide holes. The pin-hole formed end faces of the ferrules are aligned by the guide pins and abutted. The optical fibers of those ferrules, which are precisely arrayed with respect to the guide pin holes, are coupled with each other. The sides of the ferrules from which the optical fibers are led out are connected by means of a single clip. (see, Unexamined Japanese Utility Model Publication No. Hei. 2-30909)
The MT connector is advantageous in that it is simple in structure, but disadvantageous in the following. The direction for coupling the ferrules is different from the direction for clipping the ferrules. Therefore, the ferrules are coupled, and the coupled ferrules are connected by the pin. That is, two steps of connecting work are required. Thus, the connecting work is time consuming and troublesome. A connecting tool, if specially manufactured, is complicated in mechanism and structure. There is no room for mounting means additionally attached in the MT connector. As a result, it is difficult to secure a high density mounting of those connectors, or high density mounting of optical fibers, in the branch modules or the fiber termination modules.
A connector with a push-on fastening function is also used for the MT connector. An example of this is disclosed in Unexamined Japanese Patent Publication (kokai) No. Hei. 4-215608. In the disclosed connector, an MT connector and a housing containing a coiled spring are connected through an adaptor. This type of the connector is called an MPO connector. The MPO connector is advantageous in that neither of the pin connecting work nor the clipping work is required. However, it is disadvantageous in that its complicated push-on mechanism requires a large number of component parts and accordingly a large space for them, which results in difficulty in increasing the density of fiber mounting in the connector or the terminal module.
In a conventional MPO connector, ferrules are accommodated in a housing and the end faces of the optical fibers are exposed on the end faces of the ferrules. The optical fibers are bonded to the ferrules by adhesive, and then the end faces of the ferrules are polished. A couple of connectors are inserted into the connector adaptor shaped like a rectangular prism from its right and left sides, whereby the ferrules located side by side are connected to each other by two guide pins. A connector fixing mechanism is provided in the connector adaptor. An insertion guide, which is provided at the end of the housing, is engaged and fixed in the connector adaptor. The gap between the connector housing and the ferrules is a floating space.
In the MPO connector, the ferrules are connected in a PC (physical contact) where the ferrules are brought into optical contact with each other without a refractive index matching substance. The end faces of the ferrules are each slantly polished at an angle of 8.degree. relative to a plane perpendicular to the optical axis of the optical fiber. Each optical fiber is abutted against the associated one in the order of submicron by the utilization of the hardness difference between the resin materials of the optical fibers and the ferrules.
The connecting work for the MPO connector consists of one step. Further, the connector adaptor may be attached to the frame. Because of this, this type of the connector may be used for such an application as the fiber termination module. However, the MPO connector has such shortcomings that the connector size is large and hence it is impossible to increase the connector mounting density, and that the number of necessary component parts is large and hence the cost to manufacture is large.
In many kinds of optical connectors now commercially available, optical fibers are bonded for their fixing by use of epoxy or other kinds of resins as an adhesive. When such kinds of optical connectors are connected to the optical fibers in a construction site, the connector connecting work is inefficient and such a hardening tool as a heater is indispensably used. The result is an increase of fiber cable laying cost and associated cost.
Unexamined Japanese Patent Publication (kokai) No. Hei. 8-240742 proposes a solution to this adhesive problem in the connector-fiber connecting work. In the publication, the optical fiber is positioned in the groove or channel of the optical connector, and in this state it is held and fixed therein.
FIGS. 32A to 32D are explanatory diagrams for explaining the optical connector disclosed in the publication. FIG. 16A is an exploded, perspective view showing the optical connector. FIG. 16B is a sectional view of the optical connector of FIG. 16A. FIG. 16C is a sectional view showing the optical connector when an optical fiber is fixed in the optical connector. FIG. 16D is an explanatory diagram for explaining the work of fixing the optical fiber to the optical connector. In those figures, reference numeral 201a is an exposed glass fiber portion of an optical fiber; 201b is a coated fiber portion of the optical fiber; 221 is a connector body; 221a is a guide pin hole; 221b is fiber fixing grooves or channels; 221c is a wedge insertion hole; 221d is a lateral hole; 222 is a wedge; 222a is a slanted surface of the wedge; and 223 is a spring member.
An optical fiber is inserted into the connector body 221 from the back side of the connector. The exposed fiber portion 201a of the optical fiber is positioned in one of the fiber fixing grooves 221b of a V-shape in cross section. The wedge 222 is inserted into the connector body from the wedge insertion hole 221c and moved toward the lateral hole 221d. The spring member 223 is inserted into the wedge insertion hole 221c to urge the wedge 222 forward, as shown.
The optical connector is advantageous in that there is no need for using adhesive, but has the following disadvantage. After the optical fiber is inserted into the connector body, the wedge 222 is moved forward along the exposed fiber portion 201a of the optical fiber, as shown in FIG. 16D. In some state of the contact of the wedge 222 with the exposed fiber portion 201a, there is a chance that the forward movement of the wedge 222 scrapes the exposed fiber portion 201a of the optical fiber. If the exposed fiber portion is scraped, the resultant scrape will give rise to breaking of the fiber when it is used for a long time.